A cupola is a cylindrical shaft furnace that burns coke, ore or scrap steel, and limestone, intensified by the blowing of air through tuyeres to create a molten alloy of metal such as iron. Slags are:also created along with the metal or alloy as a result of the smelting of ore. Alternate layers of ore, limestone, and coke are charged into the top of the cupola. As the ore descends, the ore is melted by direct contact with the countercurrent flow of hot gasses from the coke combustion. The resulting molten metal or alloy collects in the well of the cupola where it is discharged for use by intermittent tapping or by continuous flow.
The iron which collects in the base of the cupola travels through an opening allowing the molten metal to collect in the breast or separator of the blast furnace, where slag is skimmed from the surface of the metal, depending on whether the cupola is a conventional or a dry bottom cupola. The opening is referred to as a "tap-hole" or iron exit for the cupola.
A conventional tap-hole is formed by making a form shape, usually round or rectangular, from steel and installing refractory material around the form shape during a relining of the breast or separator in the cupola. After the first tapping of the cupola, thus opening the iron exit, the steel form melts away, but its shape is maintained by the refractory, thus identifying the tap-hole in the cupola.
In U.S. Pat. No. 2,492,269, water-cooled members for blast furnaces are described. Due to the high temperatures generated in the hearth and bosh of blast furnaces, such as are used for smelting iron ore, and the erosive action of the molten iron and slag, means are provided for cooling the furnace brickwork to prolong its life. Cooling has been provided for the furnace openings through which the blast is introduced into the hearth, and through which the molten slag is drawn off between castings in order to withstand the intense physical, thermal, and chemical action. It is there indicated that water-cooled copper or bronze castings are used for these purposes, because of its high conductivity. However, copper or bronze will not withstand long contact with the molten iron or slag, sometimes resulting in burned castings whereupon water is released into the furnace causing delays. Repair is thus time-consuming and costly.
Tap-hole deformation can be caused by, but is not limited to, the high temperatures of the molten iron, the large volumes of hot blast air, mechanical erosion, and chemical erosion. As a result of one or more of these and other possible factors, the refractory lining the cupola and the tap-hole wears out and frequently must be replaced. Typically, this replacement of the refractory at the tap-hole occurs on a daily or weekly basis. Thus, it is a costly repair item in cupola operation, but practically there are no other readily available options. Thus, it continues to be a problem to reduce or eliminate the need for such costly repair.
In U.S. Pat. No. 4,498,610, a tap-hole for a melting furnace is described as including a cylindrically-shaped copper shell having a central opening through which molten material from the furnace passes. The shell includes a reduced inner diameter portion defining an orifice and a plurality of narrow holes formed in the shell wall adjacent the orifice but isolated therefrom and interconnected to form a plurality of highly restrictive flow passages. A liquid coolant is supplied to the passages. However, such a device has a number of practical drawbacks which limit its applicability, not the least of which is that the device cannot be practically installed in a cupola from a safety standpoint. If the shell ruptures, water could potentially escape to the furnace or the pouring floor with deleterious effects. In addition, the shell, to be effective, apparently needs to form a freeze of molten material, or slag, in the orifice to serve as a liner so that the freeze results in effective cooling by the resulting skin or skull on the working surface.
Thus, it remains a continuing problem in the blast furnace art to provide a method and apparatus for reducing or eliminating a need for costly and untimely repairs of the tap-hole.
It is another continuing problem in the blast furnace art to provide a method and apparatus for prolonging the life of a cupola refractory at the tap-hole area, to reduce repairs.
It is still another continuing problem in this art to provide a water-cooled member for a cupola in a blast furnace to prolong refractory life at the tap-hole area, and to reduce the occasions for repair of the refractory at that location.